The present invention relates to a film formed of a polybenzazole precursor or a polybenzazole.
A polybenzazole film formed of a polybenzazole has high strength and high modulus of elasticity; moreover, it has excellent heat resistance and flame retardance. Therefore, a large number of improved polybenzazole films, including those disclosed in the patent documents described below, have been proposed with the object of using them for novel applications, such as magnetic tapes, insulating films for electronic components, and liquid crystal alignment layers.
Japanese Laid-Open Patent Publication No. 4-202257 discloses a polybenzazole film with improved homogeneity, which is made up of a composition containing a polybenzazole and a specific polymer. Japanese Laid-Open Patent Publication No. 11-171993 discloses a polybenzazole film with improved smoothness, which has a specified surface roughness. Japanese Laid-Open Patent Publication No. 2000-273214 discloses a polybenzazole film with improved mechanical properties, which has a specified elongation and a specified Young's modulus. Japanese Laid-Open Patent Publication No. 2001-11311 discloses a polybenzazole film with improved light resistance, which contains a polybenzazole and a specific anthraquinone compound. Japanese Laid-Open Patent Publication No. 63-74612 discloses a polybenzazole film with improved tear strength, which is produce by a specific production method. Japanese National Phase Laid-Open Patent Publication No. 6-503521 discloses a mechanically oriented polybenzazole film.
In recent years, there have been demands that polybenzazole films, particularly those used for semiconductor package materials and electronic devices, have not only high strength, high modulus of elasticity, and high heat resistance, but also anisotropies such as optical anisotropy, magnetic anisotropy, mechanical anisotropy, thermal anisotropy, and electrical anisotropy. However, none of the polybenzazole films disclosed in the above patent documents has strong anisotropies.